This application in response to RFA-DA-08-016 is aimed at investigating the role of non-coding RNAs in neuroplasticity and addiction. Specifically, we seek to gain an understanding of the role of microRNAs (miRNAs) in compulsive drug seeking. miRNAs are a family of small (~22 nucleotides) noncoding RNAs that can regulate gene expression by binding to complementary sequences in target mRNA transcripts to facilitate their degradation and/or inhibit their translation. Emerging evidence suggests that miRNAs may play an important role in neuroplasticity, but their role in addiction-related behavioral deficits is unknown. Specific Aim I will involve characterization of brain expression patterns of miRNAs in an animal model of compulsive cocaine consumption. Specifically, we will examine the effects of restricted (1 h) or extended (6 h) daily access to intravenous cocaine self-administration in rats, which results in a compulsive-like escalation of daily cocaine intake, on the expression of miRNAs throughout cortical and subcortical brain regions heavily implicated in drug addiction neuropathology. In addition, we will also assess miRNA expression patterns in the same brain regions in post-mortem brain tissues from human cocaine addicts. It is predicted that compulsive cocaine seeking in rats and humans will be associated with distinct patterns of dysregulated miRNA expression. Importantly, convergent data between the rat and human tissues will provide support for the participation of particular miRNAs or families of miRNAs in addiction-related neuroplasticity. In Specific Aim II we will directly assess the relevance of the altered expression patterns of miRNAs that occur in rats compulsively seeking cocaine. Specifically, we will infuse into discrete brain regions lentiviral vectors to over-express, or locked nucleic acid (LNA)-modified antagomiRs to knock-down, targeted miRNAs. The effects of modulating targeted miRNAs in this manner will be assessed on compulsive cocaine seeking behavior in rats. Specific Aim III will involve functional characterization of miRNAs shown to modulate compulsive cocaine seeking. Here, miRNAs whose expression modulates cocaine seeking will be studied with respect to cellular localization, mechanism of regulation and identification of potential target mRNA transcripts upon which these miRNAs act. The proposed work promises to yield significant new insights into the pathophysiology of addiction, and may reveal novel treatment and/or biomarker approaches for this devastating disorder. PUBLIC HEALTH RELEVANCE: Substance abuse disorders including cocaine addiction are a tremendous health burden to society. Indeed, cocaine use is associated with potentially fatal cardiovascular events such as arrhythmias, myocardial infarction, and cerebral hemorrhage, and results in approximately $580 million in direct healthcare costs. Thus, cocaine addition results in tremendous human suffering and negative economic impact on society. Importantly, the underlying pathophysiology that drives compulsive drug seeking remains largely unknown, and there is a marked need for improved treatment paradigms. The proposed work has the potential to aid in the development of completely novel therapeutics.